A system and method for selecting a gray shade primer undercoat that would provide optimal color development of a poor hiding topcoat at less than half the film thickness of the topcoat color at complete hiding.
The method of this invention is directed to choosing a gray shade primer color such that a topcoat can be applied over the primer at less than complete hiding but still achieve optimal color development of a topcoat color. This invention provides a simple way for determining an appropriate gray shade primer color for any given top coat color.
Numerous difficulties have been encountered developing high chromaticity, or color development, in colors which, due to their nature, have poor hiding. The inventors have developed a simplified method of determining an optimum color of gray primer for a given top coat so that, even if a topcoat is applied at less than 100% hiding, no color difference can be detected visually as compared with the color of the topcoat applied at complete hiding.
Techniques have been used to select proper gray, white, or black primers in the area of auto body repair or repaint to assure that a top coat matches other parts of the vehicle that have not been repainted. For example, Abe et al, U.S. Pat. No. 4,546,007, uses a method of selecting a white, gray, or black primer whose spectral reflectance comes as close as possible to the maximum value of the spectral reflectance curve of the top coat when applied at complete hiding. The method of Abe et.al. teaches matching the color of paint that is being repaired. Also, in U.S. Pat. No. 5,700,515 to Rodrigues is disclosed a method for selecting a primer, wherein a gray primer of choice would be the one whose reflectance is the same or very close to the reflectance of the topcoat at the wavelength of minimum absorption of the top coating. However, architectural products have different application challenges than automotive applications, such as banding and roller overlap of topcoat colors, which create unevenness in the coating appearance.
To overcome the above challenges of architectural coatings, it has been found that gray shade primers, when used as an undercoat, can provide reproducible and consistent topcoat color hiding and color development. The use of this system provides optimized color gamut, film integrity and hiding, and dramatically improves touch-up which are primary concerns in the architectural coatings industry. Use of a gray shade primer helps prevent banding (also known as picture framing) and roller overlap (lap marks) in roller application. The use of a gray shade primer according to this invention also prevents a mottled or grainy film appearance, so the color maintains a uniform appearance with the elimination of micro-variations.